Roadway marking tapes have advantages over painted markings on roadways. Those advantages include more effective reflective properties, potential removability, and a potentially longer service life. The use of various types of polymeric sheeting products in roadway marking tapes has been known for years.
Some of the deficiencies associated with known pavement marking tapes include (1) conformance difficulties; (2) limited temperature ranges for application to a highway surface; (3) environmental and health concerns associated with the production of the marking tapes (particularly concerns about solvent vapors generated during production); (4) high production cost (specifically, raw material costs and waste due to difficulties in controlling complex production processes); and, for temporary markings, (5) inadequate mechanical properties (tensile strength) for removability.
The practical significance of inadequate conformance is a tendency toward inadequate initial or permanent adhesion of the marking tape to the roadway surface. The nonconformant or elastic nature of some tapes may result in a tendency toward recovery of initial shape after the tape has been deformed by tamping during application. If the tendency to recover exceeds the adhesive force attaching the tape to the pavement, detachment occurs. Once a marking tape becomes prematurely detached from the roadway surface, advantages such as more effective reflective properties and potentially longer service life can not be realized.
Adhesion problems are often exacerbated by rain on the highway surface. Water in small pockets between the tape and the roadway surface may act to hydraulically lift the tape from the roadway surface especially when under the action of traffic and/or freezing and thawing environmental conditions.
Previous approaches to improved conformance of marking tapes employed either metallic foil or nonvulcanized-rubber base layers. Softer, more easily conformable and less elastic tapes gain an improved adhesion to the roadway surface but suffer from reduced durability and are subject to relatively rapid wear by traffic. Additionally, such materials are characterized by low tensile and tear strength and, thus, are generally unsuitable as removable, temporary pavement marking tapes. Often additional components, such as nonwoven fabric, are added to enable removability. Such materials increase the cost of the marking tape.
Mineral particulates have been used previously in polymers as fillers to reduce costs; as reinforcements to increase mechanical properties (tensile strength, tensile modulus, and hardness) or improve thermal properties; and as extenders to partially substitute for costly pigments such as titanium dioxide. Generally, finer particulates have been favored as extenders and reinforcements. The applicants are unaware of the prior use of particles in thermoplastic materials to form composites with improved conformance properties for roadway marking tape.
For years, the typical method of attachment of reflective beads and, optionally, skid-resisting particles to road marking tapes has been embedding of the beads and/or skid resisting particles into uncured polymeric systems or dissolved polymers. Each of these attachment processes suffers from a disadvantage. For example, if a solvent system is employed, the production of solvent vapors must be handled. Solvent vapors are increasingly of environmental and health concern in production facilities.
Another concern with removable temporary pavement marking tapes is a disposal concern. Waste materials which include chlorinated hydrocarbons are increasingly looked upon with disfavor for landfill disposal or incinerator disposal.
In view of the above-described deficiencies associated with known marking tapes or sheets, a desirable marking sheet would embody the following properties:
Excellent conformance to the substrate surface
Extended temperature range for application
Removability
Reduced disposal concerns
Solvent-less or near solvent-less production
Lack of dependence on critical reaction kinetics for bead bonding
Reduced raw material costs
Acceptable durability
The present invention, as disclosed below, satisfies these requirements and includes new pavement marking sheets, processes for manufacturing the marking sheets, and a new composite material of the sheet.